Methods and apparatuses for pump sealing during leakage events

ABSTRACT

A pump leakage mitigation device includes one or more clamp arms on an outer surface of a pump that can be driven by a biasing element to seat against a shaft of the pump to seal or reduce fluid flow through a breakdown of the pump. The biasing element engages only at threshold temperatures, such as those associated with breakdown orifice failure when additional sealing may be necessary. Clamp arms of any number and shape can be used to achieve the desired seal and based on the pump geometry. A sealant surface and/or keeping mechanism are useable with the leakage mitigation device to enhance fluid flow blockage throughout a pump failure transient scenario. Pump leakage mitigation devices are installed on an outside of a variety of different pump types and can thus be installed, actuated, manipulated, disengaged, and/or removed without having to destroy or disassemble the pump.

RELATED APPLICATIONS

This application is a divisional of, and claims priority under 35 U.S.C.§§ 120 & 121 to, co-pending U.S. application Ser. No. 13/340,675, nowU.S. Pat. No. 10,777,329, filed Dec. 30, 2011, which is incorporated byreference herein in its entirety.

BACKGROUND

FIG. 1 is an illustration of a conventional light water reactorrecirculation pump 10 used to drive coolant/moderator through a nuclearreactor. As shown in FIG. 1, pump 10 includes a shaft 11 that drives acentrifugal or other pump mechanism 19 to create a pressure head orfluid injection into a nuclear reactor. Conventional recirculation pump10 includes a seal cartridge 12 through which shaft 11 extends. Sealcartridge 12 may generally separate shaft 11 into regions that areimmersed in driven fluid, such as at pump mechanism 19, and regions thatare dry and receive driving mechanical energy, such as a top portion ofshaft 11. A breakdown orifice 13 where shaft 11 passes into sealcartridge 12 may generally prevent or substantially reduce migration offluid from pump mechanism 19 up along shaft 11 and outside sealcartridge 12. In this way, conventional recirculation pump 10 may drivecoolant/moderator through a reactor without loss of coolant/moderatorthrough the pump.

As shown in FIG. 1, some conventional recirculation pumps 10 inpressurized water reactors may include one or more internal organicshutdown seals 15 that may be installed through disassembly of the pump.During non-use of pump 10, such as during maintenance periods or certaintransient events like a station blackout, temperatures and pressure of aworking fluid through pump mechanism 19 may cause breakdown orifice 13to leak coolant/moderator. Internal organic shutdown seals 15 mayinclude a separate thermal actuator that releases organic o-rings topermanently seal against and/or adhere to shaft 11 within seal cartridge12 at a temperature associated with failure of breakdown orifice 13,thereby preventing or reducing leakage along shaft 11 and eventuallybreakdown orifice 13 caused by temperatures and pressure within thereactor. The organic o-ring may require replacement at time intervalsassociated with plant outages.

SUMMARY

Example embodiments include devices for reducing leakage of fluidsthrough pump breakdown orifices and pumps using the same. Exampleembodiments are useable with pumps having a drive shaft passing into thepump through an orifice that may leak or otherwise fail at highertemperatures. Such pumps would include, for example, recirculation andemergency cooling pumps used in commercial nuclear reactors worldwide.Example embodiments include at least one clamp arm on an outer surfaceof the pump that can be driven by a force to seat against the shaft andblock the breakdown orifice at temperatures where such sealing may benecessary. The force can be provided by any type of biasing element thatactuates based on temperature, including a thermocouple-actuator pairingor bimetallic spring, for example. Single or several clamp arms may beused to achieve the desired seal and based on the pump geometry. Forexample, two clamps having semi-circular surfaces or a single cinchclamp may effectively seal a perimeter of a round pump shaft.

Because clamp arms are seated against a shaft at a breakdown orificeonly at desired temperatures, example embodiments may be actuated atthreshold temperatures associated with breakdown orifice failure, suchas approximately 300-350 degrees Fahrenheit, for example, to engage andhelp mitigate fluid losses through breakdown orifices only in failureconditions. Further, because example embodiments may be deployed onexternal portions of pumps, example embodiments may be installed,accessed, and removed without having to destroy or disassemble the pump.Example embodiments may use radiation and temperature resilientmaterials that do not require replacement.

Example embodiments may include several additional features to enhance aseal and perform in desired manners. For example, a clamp arm caninclude a sealant surface like a gasket or adhesive that enhancescontact between the arm and shaft/breakdown orifice and further reducesleakage. Example embodiments can also use keeping devices like ratchets,locks, etc. to maintain a clamp arm in a sealing position once actuated.If a passive biasing element like a bimetallic spring is used, keepingdevices may maintain the enhanced breakdown orifice seal even after apump starts to cool down. Additional elements are also useable exteriorto the pump, such that they may be installed, disengaged, and/or removedwithout needing to disassemble the pump.

BRIEF DESCRIPTIONS OF THE DRAWINGS

Example embodiments will become more apparent by describing, in detail,the attached drawings, wherein like elements are represented by likereference numerals, which are given by way of illustration only and thusdo not limit the terms which they depict.

FIG. 1 is an illustration of a conventional recirculation pump useablein nuclear reactors.

FIG. 2 is an illustration of a side view of an example embodimentrecirculation pump seal.

FIG. 3 is an illustration of a top view of an example embodimentrecirculation pump seal.

DETAILED DESCRIPTION

This is a patent document, and general broad rules of constructionshould be applied when reading and understanding it. Everythingdescribed and shown in this document is an example of subject matterfalling within the scope of the appended claims. Any specific structuraland functional details disclosed herein are merely for purposes ofdescribing how to make and use example embodiments. Several differentembodiments not specifically disclosed herein fall within the claimscope; as such, the claims may be embodied in many alternate forms andshould not be construed as limited to only example embodiments set forthherein.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another. For example, a first element could be termed asecond element, and, similarly, a second element could be termed a firstelement, without departing from the scope of example embodiments. Asused herein, the term “and/or” includes any and all combinations of oneor more of the associated listed items.

It will be understood that when an element is referred to as being“connected,” “coupled,” “mated,” “attached,” or “fixed” to anotherelement, it can be directly connected or coupled to the other element orintervening elements may be present so long as this does not destroy anyfunctionality of the described features. In contrast, when an element isreferred to as being “directly connected” or “directly coupled” toanother element, there are no intervening elements present. Other wordsused to describe the relationship between elements should be interpretedin a like fashion (e.g., “between” versus “directly between”, “adjacent”versus “directly adjacent”, etc.).

As used herein, the singular forms “a”, “an” and “the” are intended toinclude both the singular and plural forms, unless the languageexplicitly indicates otherwise with words like “only,” “single,” and/or“one.” It will be further understood that the terms “comprises”,“comprising,”, “includes” and/or “including”, when used herein, specifythe presence of stated features, steps, operations, elements, ideas,and/or components, but do not themselves preclude the presence oraddition of one or more other features, steps, operations, elements,components, ideas, and/or groups thereof.

It should also be noted that the structures and operations discussedbelow may occur or be present out of the order described and/or noted inthe figures. For example, two operations and/or figures shown insuccession may in fact be executed concurrently or may sometimes beexecuted in the reverse order, depending upon the functionality/actsinvolved. Similarly, individual operations within example methodsdescribed below may be executed repetitively, individually orsequentially, so as to provide looping or other series of operationsaside from the single operations described below. It should be presumedthat any embodiment having features or functionality described below, inany workable combination, falls within the scope of example embodiments.

FIG. 2 is an illustration of an example embodiment temperature-dependentbreakdown orifice seal 100 installed about a breakdown orifice 13 of apump. As shown in FIG. 2, example embodiment seal 100 includestemperature-sensitive biasing element 110 coupled to a sealing clamp120. Both biasing element 110 and sealing clamp 120 are shaped and sizedto be installed about a breakdown orifice 13 of a selected pump. Forexample, biasing element 110 may be connected between a support of sealcartridge 12 and sealing clamp 120, and sealing clamp 120 may beslidably installed on a top surface of seal cartridge 12 connected tobiasing element 110. Or, for example, biasing element 110 may beconnected between another nearby static structure and sealing clamp 120.Because example embodiment temperature-dependent breakdown orifice seal100 is installed with sealing clamp 120 exterior to seal cartridge 12,such as about breakdown orifice 13, example embodiment seal 100 may beinstalled, accessed, removed, and/or manipulated without needing todisassemble or destroy seal cartridge 12 and/or a pump including thesame.

Temperature-sensitive biasing element 110 is configured to bias sealingclamp 120 in a manner to seal or substantially block breakdown orifice13 when a pump reaches a threshold temperature. The thresholdtemperature may be chosen to correspond to breakdown orifice 13 failureand/or leakage temperatures. For example, element 110 may be abi-metallic spring that experiences thermal expansion at temperaturesassociated with overheat and likely failure of breakdown orifice 13. Thethermal expansion may cause such a bimetallic spring to push sealingclamp 120 away from a relative static structure to which the spring isattached and toward shaft 11.

As a specific example, normal operating temperatures of seal cartridge12 and thus example embodiment orifice seal 100 may be approximately100-130 degrees Fahrenheit. During a loss of power event associated withloss of reactor cooling, temperatures may relatively quickly rise andapproach 535 degrees Fahrenheit. In such an example, a bi-metallicspring useable for temperature-sensitive biasing element 110 may bechosen of materials that discriminately expand and thus bias clamp 120at threshold temperatures above normal operating temperatures of 100-130degrees Fahrenheit, for example, at around 250-300 degrees Fahrenheit.In this way, clamp 120 may not be biased at operating temperatures orminor overheat conditions but will be biased and remain biased attemperatures associated with lengthy transients causing failure andleakage through breakdown orifice 13. This may prevent clamp 120 fromcontacting shaft 11 during operation and thus prevent or reducepotential for damage from contact between a rotating shaft 11 and clamp120.

Other threshold temperatures for temperature-sensitive biasing element110 may be desired and achieved. If biasing element 110 is a bimetallicspring, for example, appropriate material selection and configurationmay produce engagement at other threshold temperatures to account fordiffering steady-state operating temperatures and/or breakdown orifice13 failure temperatures. Similarly, other types of temperature-sensitivebiasing elements 110 are useable in example embodiments aside frombimetallic springs, including temperature-sensitive actuators orthermocouples and transducers, for example. Bi-metallic springs andsimilar mechanisms may offer an advantage of requiring no external powerto operate, being fabricated of materials that are resilient againstconditions found in operating nuclear plants, and/or being relativelyeasy to install on seal cartridges 12 of various types of pumps found inconventional nuclear power plants.

Clamp 120 may take on several different configurations in order tosuccessfully seal and/or reduce leakage through a failed breakdownorifice 13. As shown in FIG. 3, two example embodimenttemperature-dependent breakdown orifice seals 100 may be installed onseal cartridge 12 on opposite sides of shaft 11 with crescent-shapedclamps 120 to seat against shaft 11. Alternatively, a single exampleembodiment orifice seal 100 may be used with a clamp 120 that may be acinch clamp that seals an entire perimeter of shaft 11 about breakdownorifice 13. Any number of clamps 120 of various shapes and/ortemperature-sensitive biasing elements 110 in any association withclamps 120 may be used to provide a desired geometry and achieve adegree of seal to breakdown orifice 13.

Clamp 120 and biasing element 110 may be fabricated of any material thatsubstantially maintains its physical properties in an operating nuclearplant and successfully blocks or seals breakdown orifice 13 whenengaged, including stainless steel, aluminum alloys, carbon steel, etc.If resilient materials are used, example embodiments may require littleor no maintenance or replacement throughout the life of an associatedpump. Similarly, clamp 120 and biasing element 110 may be chosen of amaterial that is compatible with, and does not foul, biasing element 110and/or a surface of seal cartridge 12. As shown in FIG. 3, clamps 120may include a sealant surface 125 that may act as a gasket to enhance aseal between clamps 120, shaft 11, and/or seal cartridge 12 aboutbreakdown orifice 13. For example, sealant surface 125 may be a rubber,magnetic, plastic, and/or adhesive layer attached to a contact surfaceof clamp 120.

As shown in FIG. 3, example embodiment orifice seal 100 may furtherinclude a keeping device 130 that locks clamp 120 into a sealingposition once temperature-sensitive biasing element 110 has actuated andbiased clamp 120 to seal breakdown orifice 13. For example, keepingdevice 130 may include a ratchet surface 131 installed on clamp 120 anda corresponding ratchet keeper 132 installed on seal cartridge 12 oranother relative surface. Ratchet keeper 132 and ratchet surface 131 maybe relatively positioned to engage and lock only once clamp 120 hasmoved to a substantially-biased position against shaft 11, such as aposition required to effectively seal or block over 90% of flow throughbreakdown orifice 13 in the case of a loss of reactor coolant or otherleakage situations.

By locking example embodiment orifice seals 100 in an actuated positionagainst shaft 11 and breakdown orifice 13, even if a pump begins to cooldown and/or biasing element 110 fails after engagement, breakdownorifice 13 will remain substantially sealed by example embodiments andthus have reduced leakage post-failure and during cooldown. Ratchetkeeper 132 may then be manually, automatically, or remotely released todisengage example embodiments if additional sealing of breakdown orifice13 is no longer necessary. Such disengagement of example embodiments ispossible without destroying or dismantling seal cartridge 12 or otherpump components if external positioning is used for example embodiments.

Example embodiment temperature-dependent breakdown orifice seal 100 maybe installed on any new or existing pump where leakage along shaft 11and through breakdown orifice 13 is a risk in circumstances such asoverheat and/or overpressure of a working fluid for the pump. Becauseexample embodiments are functional on an exterior of seal cartridge 12,example embodiment temperature-dependent breakdown orifice seal 100 maybe installed, removed, and/or locally disengaged at any time a pumphaving seal cartridge 12 is accessible. Example embodimenttemperature-dependent breakdown orifice seal 100 may be installed in anynumber and clamp/biasing element configuration that meets breakdownorifice sealing needs.

Because example embodiment temperature-dependent breakdown orifice sealsare capable of installation on an exterior of a seal cartridge 12, canbe configured to selectively engage at desired temperatures, and/or arecapable of non-destructive installation, engagement, disengagement, andremoval, example embodiments may be relatively easily deployed to limitpotential leakage through breakdown orifices of a variety of existingpumps in nuclear power plants in the instance of loss of reactor coolingand breakdown orifice 13 failure. For example, reactor recirculationpumps, Reactor Core Isolation Cooling (RCIC) pump or higher-output HighPressure Injection Cooling (HPIC) pump are all useable with exampleembodiments in boiling water reactors.

Example embodiments and methods thus being described, it will beappreciated by one skilled in the art that example embodiments may bevaried and substituted through routine experimentation while stillfalling within the scope of the following claims. For example, althoughsome example embodiments are described as passively engaging at desiredtemperatures, example embodiments are equally useable with temperaturesensors that fairly directly measure temperature in pumps, such asthermocouples or thermal energy radiance monitors, and actuate atthreshold temperatures. Further, it is understood that exampleembodiments and methods can be used in connection with any reactor wherepumps may fail and leak during accident scenarios, such as a stationblackout transient. Such variations are not to be regarded as departurefrom the scope of the following claims.

What is claimed is:
 1. An external seal for a nuclear power plant pumphaving a shaft and breakdown orifice about the shaft, the sealcomprising: a clamp arm shaped to seat against the shaft at thebreakdown orifice so as to seal the breakdown orifice; and atemperature-dependent biasing element coupled to the clamp arm, whereinthe biasing element is configured to drive the clamp arm toward theshaft only at a temperature associated with failure of the breakdownorifice.
 2. The external seal of claim 1, wherein thetemperature-dependent biasing element is a bimetallic spring.
 3. Theexternal seal of claim 2, wherein the temperature is approximately 300degrees Fahrenheit.
 4. The external seal of claim 1, wherein the clamparm includes a crescent shape matching an exterior of the shaft.
 5. Theexternal seal of claim 4, further comprising: a sealant surface attachedto the clamp arm, wherein the sealant surface is configured to enhancethe sealing of the breakdown orifice.
 6. The external seal of claim 1,further comprising: a keeping device configured to lock the clamp arm ina position sealing the breakdown orifice.
 7. The external seal of claim6, wherein the keeping device includes a ratchet surface on the clamparm and a ratchet keeper stationary to the clamp arm and positioned toengage the ratchet surface.
 8. The external seal of claim 6, wherein thekeeping device is configured to be released without dismantling thepump.